Proposed studies are designed to examine the ultrastructure of selected areas of the brain and pituitary gland of rodents and amphibians after administration of endogenous opiate peptides and specific neurotoxins. Cells of the pars intermedia, and neurons and fibers of the ventral hypothalamus, including the median eminence, will be studied with transmission electron microscopy for effects of in vivo injections of synthetic endorphins and enkephalins, and 6-hydroxydopamine and p-chloroamphetamine. Scanning electron microscopy will be used to observe effects of the procedures on surface cells of the third ventricle of the brain in both species. Morphologic changes, observed in brain endocrine cells, will provide additional data on the actions of the intrinsic opiate peptides at the cellular level on a comparative basis.